The aim of this project is to increase our understanding of the neural bases of adaptive mechanisms responsible for maintaining appropriate performance of the oculomotor system. Previous work had already described an adaptive control mechanism for rapid, or saccadic, eye movements. This adaptive mechanism has two components: one which maintains saccadic accuracy and one which suppresses postsaccadic ocular drift. Hence, working in concert, these two components assure that saccadic eye movements accurately acquire visual targets and that these movements end abruptly, allowing clear vision. Both of these adaptive components depend upon an intact cerebellum. The mechanism for maintaining saccadic accuracy appears to be localized in the area of the posterior cerebellar vermis and paravermis. In this project the component of the adaptive mechanisms responsible for suppression of postsaccadic ocular drift were studied in detail. It was shown that full-field visual slip was sufficient to elicit adaptation in normal monkeys. This adaptive response was then studied in two monkeys with complete bilateral ablations of the flocculus of the cerebellum. The results showed that the ability of the brain to respond to the retinal slip following saccades had been reduced over tenfold.